Excellent article - as another poster said, this one is a keeper. Even if one uses a subnet calculator program like SolarWinds it is still good to go back and review the basics.
The CCNA program I took at Sacramento City College drummed subnetting into our heads almost ad-nauseum, but I'm glad they did. I can almost (notice I said "almost") do subnetting in my head.
Also, thanks for making the article a downloadable PDF - good to keep on the laptop for reference.
Keep Up with TechRepublic